Like people have already stated this has been done before, the solo white mage is actually one of the easier Solo games to do. The solo theif no class change being the hardest (*Has completed em all*). Anyway, good luck. Make sure you get RUSE, CURE and MUTE. The three most important spells to have in a solo white mage game.

Oh and btw, I think someone over at the gamefaqs message board has even beat a level 18 or so solo white mage. I think it was sqpat.